1. Field of the Invention
The present invention relates to rotational speed control of internal combustion engines, and more particularly to methods and systems for reducing pulsations in the rotational speed of such engines.
2. Description of the Related Art
In a motor vehicle, pulsations in the rotational speed of the engine, particularly at engine idle, can be a source of customer dissatisfaction. In such a vehicle, an engine controller will (among its other engine control duties) attempt to control the idle speed of the engine to a predetermined target value. However, the torque produced by the engine is a complicated non-linear function of many variables, including the rotational position of the engine. Thus, pulsations in idle speed about the predetermined target value occur despite attempts by the engine controller to control the idle speed to the target value.
Using an electrical machine as a supplemental torque source to improve idle speed control and reduce engine speed pulsations is known and has been investigated in recent years. For example, in "Vehicle Idling Variation Reduction Using Electric Machine Active Torque Control", Japan Society of Mechanical Engineers Proceedings, volume 59, no. 560 (1993-4), a method is presented for estimating angular velocity and angular acceleration of the engine and controlling a supplemental torque source to provide torque which cancels the torque variations of the engine. However, such estimates, particularly the estimate of angular acceleration, can be very computationally complex and can introduce sensitivity to noise.
A method and system whereby a supplemental torque source reduces engine speed pulsations in a very effective and computationally efficient manner will provide considerable advantages. When applied in a motor vehicle at idle, such a system and method will improve customer satisfaction with the idle quality of his vehicle.